The present invention relates generally to an advanced static VAR (volt amperes reactive) compensator (ASVC) control system, and more particularly to an ASVC control system including a method and an apparatus for compensating reactive power losses of alternating current (AC) power transmission lines.
Delivering power from a power generating station to the ultimate power consumers over long transmission power lines can be very costly for an electric utility. The electric utility passes on these costs to the ultimate consumers as higher electricity bills. These costs stem from two types of power losses. The first is a real power loss in watts from heating of the power lines, often referred to as "I.sup.2 R" losses. The second loss component stems from the magnetic effects of the power flowing through the transmission lines, which are referred to as inductive and capacitive losses. These inductive and capacitive losses affect a reactive component of the power which is measured in volt-ampere-reactive (VAR) units. These reactive (VAR) losses may be compensated using a static VAR compensator to more economically transmit power to the ultimate consumers and reduce their electricity bills.
Generally, static VAR compensators are based on the concept that inverters of various types can be connected between an AC power transmission line and an energy-storage device. The energy storage device may be an inductor or a capacitor. The static VAR compensator is operated to draw a purely reactive current from the power lines at its point of connection. Typically, the static VAR compensator has an inverter with gate-controlled power switching devices, such as gate turnoff thyristors (GTO). For transmission line implementations, the volt-ampere (VA) rating of the inverter is typically far higher than the rating normally encountered for industrial inverters.
The effect of a static VAR compensator is analogous to the well-known operation of a rotating synchronous condenser or a static VAR generator using thyristor-switched capacitors. Static VAR compensators are useful for maximizing the transmitted power and improving the stability of the utility system. Apart from the complexity of the power electronics of the inverter, the operation of a static VAR compensator under balanced, steady-state conditions is essentially identical to the operation of the rotating synchronous condenser when operating under steady-state conditions. However, the dynamic behavior of a static VAR compensator is more complicated than that of the rotating synchronous condenser. Previous static VAR compensators, rotating synchronous condensers, and static VAR generators have been unable to respond to the rapidly changing conditions of a dynamic power line disturbance, and thus, have performed poorly under dynamic conditions. Furthermore, the earlier static VAR compensators have been quite expensive, in terms of both initial manufacture and operational costs.
Thus, a need exists for an improved advanced static VAR compensator control system for compensating power lines to decrease power transmission costs, which is directed toward overcoming and not susceptible to, the above limitations and disadvantages.